System and method for the continuous detection of impacts on pipelines for the transportation of fluids, particularly suitable for underwater pipelines

ABSTRACT

A system and method for continuous detection of impacts on pipelines for fluid transportation, particularly on pipelines placed on the seabed. The system includes at least two sensors each installed in correspondence with an end of a section subject to detection of a pipeline. A first sensor of the at least two sensors is configured to detect first acoustic waves, which propagate along a first transmission phase associated with the pipeline, and a second sensor of the at least two sensors is configured to detect second acoustic waves which propagate along a second transmission phase associated with the pipeline. The second acoustic waves have different elastic features with respect to the first acoustic waves.

The present invention relates to a system and method for the continuousdetection of impacts on pipelines used for the fluids transportation,particularly on pipelines positioned on the seabed.

For detecting impacts on pipelines used for the fluids transportation,the use is currently known, a plurality of acoustic sensors distributedalong the length of the pipeline, suitable for detecting the presence ofwaves generated by an impact in the fluid inside the pipeline.

The use of sensors such as hydrophones or alternatively accelerometers,for example, is known.

As schematically illustrated in FIGS. 1 a and 1 b, the position andinstant of the impact 101 are determined on the basis of surveyseffected by two hydrophones 102 or two accelerometers 102′ situated atthe two ends of a section subject to the length x of a pipeline 103 in,which the impact 101 takes place. The wavefronts 104,104′ generated bythe impact 101, propagating homodirectionally in the fluid away from thegeneration point, move, in fact, in both directions along thedevelopment of the pipeline 103, reaching the two sensors 102, 102′ intimes depending on the relative distance between the same and the impactpoint.

On the basis of the time difference between the surveys of the arrivalsof the two wavefronts 104, it is possible to determine the relativedistance between the impact point 101 and the two sensors 102,102′, theintensity of the impact and also the generation instant of thewavefronts.

This detection system and method are particularly suitable for easilyaccessible pipelines. In the case of hydrophone systems, for example,the sensors must be installed along the whole development of thepipeline so as to be in contact with the fluid inside the same. Also inthe case of accelerometer systems, the sensors must be installed alongthe whole development of the pipeline and in particular, so as to be indirect contact with the outer surface of the same.

For the detection, the pipeline is divided into a plurality of sectionssubject to detection x having a length corresponding to the detectionrange of the particular sensor used, which in the case of hydrophonesand accelerometers corresponds to about 20-50 km, and the sensors areinstalled at the ends of the sections subject to detection defined.

Although this system provides good detection results in terms ofprecision and survey delays, it cannot be used in the case ofinstallations which are not easily reached.

In the case of underwater pipelines, for example, the installation ofhydrophones or accelerometers along the section of pipelines positionedand possibly laid on the sea bottom would lead to an alteration in thestructure or coating of the pipelines, thus weakening the wholetransportation system which would no longer be integral.

Furthermore, sensors installed on the seabed would create eitherproblems relating to the feeding or also considerable maintenanceproblems, considering the difficult accessibility to these.

These systems, moreover, cannot be applied to underwater pipelinesalready launched, as the positioning of the sensors along the section ofpipeline positioned on the sea bottom is extremely difficult.

The installation of hydrophones for detecting impacts on underwaterpipelines could be effected in correspondence with the two starting andarrival shores, the distance between the shores however is generallysuch as to define a detection section having a much greater length thanthe capacity of the sensors. It would therefore not be possible todetect signals useful for determining the position, intensity and impactinstant at the two ends of such a detection section.

The systems currently known cannot therefore be used for detectingimpacts on underwater pipelines.

There is however a great necessity for monitoring impacts along thesections of pipelines installed at the sea bottom, and in particular inthe section close to the shore.

In underwater pipelines, it is currently possible to only detect thepresence of an impact which causes damage to the pipe by determining theleakage of fluid being transported, corresponding to a lack of ordecrease in the pressure of the same at the receiving end, or by thesighting of leakages emerging on the surface.

The known systems for detecting impacts on pipelines for the fluidstransportation, moreover, cannot be applied to pipelines which are onlyaccessible on one side, such as for example risers in production linesfrom underwater reservoirs. In these pipelines, a detection sectionhaving both ends accessible, in correspondence with which acousticsensors can be installed is not in fact available.

An objective of the present invention is to overcome the limitationsdescribed above and in particular to conceive a system for thecontinuous detection of impacts on pipelines for the transportation offluids which can also be effectively applied to underwater installationsof pipelines.

Another objective of the present invention is to provide a system forthe continuous detection of impacts on pipelines for the fluidstransportation which can be easily installed as it does not require thepositioning of sensors along sections of pipeline positioned at the seabottom.

A further objective of the present invention is to provide a system forthe continuous detection of impacts on pipelines for the transportationof fluids which can also be used for pipelines accessible from one sideonly.

Last but not least objective of the present invention is that ofconceiving a method for the continuous detection of impacts on pipelinesfor the transportation of fluids which guarantees a high detectionprecision of both the position in which the impact has taken place andalso the instant and intensity of the impact in order to determine theentity of damage suffered by the pipeline.

These and other objectives according to the present invention areachieved by providing a system and a method for the continuous detectionof impacts on pipelines for the transportation of fluids as specified inthe independent claims.

Further characteristics of the system and method are object of thedependent claims.

The characteristics and advantages of a system and method for thecontinuous detection of impacts on pipelines for the transportation offluids according to the present invention will appear more evident fromthe following illustrative and non-limiting description, referring tothe enclosed schematic drawings, in which:

FIG. 1 a is a schematic representation of detection of an impact on anunderground pipeline monitored by means of a first known system, basedon the use of hydrophones, for revealing impacts on pipelines for thetransportation of fluids;

FIG. 1 b is a schematic representation of a detection of an impact on anunderground pipeline monitored by means of a second known system, basedon the use of accelerometers, for revealing impacts on pipelines for thetransportation of fluids;

FIG. 2 is a schematic representation of the detection of an impact on apipeline monitored by means of the system for the detection of impactson pipelines for the transportation of fluids according to the presentinvention;

FIG. 3 is a schematic illustration of the system of FIG. 2 installed ona pipeline having an underwater section;

FIG. 4 is a block scheme of the method for the detection of impacts onpipelines for the transportation of fluids according to the presentinvention.

With reference to the figures, these show a system for the continuousdetection of impacts on pipelines for the transportation of fluids,indicated as a whole with 10.

The system 10 according to the present invention comprises at least twosensors 11, 12, each installed in correspondence with at least one endof a section length (x) of a pipeline 13 wherein a first sensor 12, ofthe at least two sensors, is suitable for detecting first acoustic waves14 which propagate along the mantle of the pipeline 13 and a secondsensor 11, of the at least two sensors, is suitable for detecting secondacoustic waves 15 which propagate in the fluid inside the pipeline.

The first sensor 12 is preferably a vibro-acoustic sensor, for examplean optical fibre sensor or a longitudinal and/or transversalaccelerometer, capable of detecting the vibratory motion 14 propagatesalong the mantle of the pipeline 13 generated by an impact 16 within adetection range x, for example having a length of up to about 50 km.

Analogously, the second sensor 11 is a hydrophone capable of detectingthe presence of a wavefront 15 also generated by the same impact 16,which propagates inside the fluid along the development of the pipeline13.

The installation of the at least two sensors 11, 12 suitable fordetecting acoustic waves having different wave characteristics, and inparticular different propagation rates and/or attenuation degrees, asthey are propagated in different means, allows an accidental impact 16to be detected, which has taken place on said section x of the pipeline13, in terms of position, impact instant and intensity also when bothsensors 11, 12 are positioned at the same end of the section length x asillustrated in FIG. 2.

In particular, the section subject to detection x monitored has a lengthequal to the capacity of said sensors 11, 12.

The position, generation instant and intensity of the impact 16 aredetermined by means of a correlation between the signals registered byboth sensors 11, 12. The waves, in fact, propagate in the fluid andalong the mantle of the pipeline 13 with different propagation rates andattenuation degrees, thus reaching the respective sensors 11, 12 atdifferent times and intensities, also when these are substantiallysituated in the same position.

If the propagation rates v₁,v₂ and degree of attenuation of thevibro-acoustic waves in the two means (fluid and mantle) are known, itis possible to determine the relative distance between the impact point16 and said sensors 11, 12, in addition to the formation instant andinitial intensity of the same 16 on the basis of the time difference anddifference in intensity of the signals revealed by the two sensors 11,12.

The propagation rates and degree of attenuation of the vibro-acousticwaves are linked to the materials in which they are diffused and can bemeasured a priori for each of these.

The sensors 11, 12 are preferably arranged in the same position of thepipeline, but the system also functions perfectly when the sensors 11,12 are at a distance from each other, for example if they are positionedat opposite ends of the section subject to detection x.

The system 10 according to the present invention, can also comprise agreater number of detection sensors 11, 12 substantially positioned incorrespondence with at least one end of a section subject to detectionx, in order to increase the degree of accuracy of the surveys.

FIG. 3 illustrates a possible application of the system 10 for thedetection of impacts on underwater pipelines for the transportation offluids according to the present invention, wherein a pipeline 13 has atleast a first underground, section 13 a upstream, a second section 13 bwhich is close to ground level and is positioned in correspondence witha shore, and also a third underwater section 13 c.

Using the simple positioning of the two sensors 11, 12, suitable fordetecting acoustic waves having different wave characteristics incorrespondence with the second section of pipeline 13 b, it is possibleto detect the position, generation instant and intensity of possibleimpacts which take place in the underwater section 13 c.

Possible impacts along the first underground section of pipeline 13 acan be possibly revealed through traditional systems of the known type,such as, for example, those illustrated in FIGS. 1 a and 1 b.

Furthermore, for the installation of the system 10, it is preferable butnot necessary for there to be a section of pipeline 13 b emerging fromthe ground, as the sensors 11, 12 can also be installed in anunderground section of pipeline 13 a.

The functioning of the system 10 for the continuous detection of impactson pipelines for the transportation of fluids is described hereunder onthe basis of the embodiment illustrated, wherein both sensors 11, 12 aresituated in substantially the same position in correspondence with thesame end of a section subject to detection x.

When impacts 16 takes place, the acoustic waves are generated, whichpropagate in both the fluid inside the pipeline 13, and also along themantle of said pipeline 13. When propagating along the mantle of thepipeline 13, a first acoustic wave 14 reaches the first sensor 12 which,as it is continuously perceptive, detects the arrival of the firstacoustic wave 14 and generates a first corresponding signal (phase 110).

After a time interval Δt, when there is the arrival of a second acousticwave 15 which propagates through the fluid inside the pipeline 13, thesecond sensor 11—also continuously perceptive—detects said arrival andgenerates (phase 120) a,second signal.

The time interval Δt of the arrival of the two acoustic waves 14, 15 isthen determined (phase 130) and using the same Δt, the impact 16 islocalized (phase 140) by determining the distance d between the twosensors 11, 12 and the point in which the impact has taken place.

In the particular configuration of FIG. 2, in which the first sensor 12and second sensor 11 are substantially in the same position, thedistance d is calculated on the basis of the following equation:

d=((v ₁ *v ₂)/Δv)*Δt

where v₁ and v₂ are the propagation rates of the acoustic waves alongthe mantle of the pipeline 13 and in the fluid inside the 13 itself,respectively, and Δv is the difference between the two rates v₁,v₂.

Once the distance d has been determined, it is possible to determine thegeneration instant of the impact starting for example from the instantof arrival of the first acoustic wave 14 in correspondence with thefirst sensor 12 and subtracting the interval determined from the ratiobetween the calculated distance d and the propagation rate v₁ of theacoustic waves along the mantle of the pipeline 13 (phase 150).

Analogously, it is possible to determine the initial intensity of theimpact 16, by adding to the intensity revealed, the attenuation in therespective propagation phase calculated by multiplying the attenuationindex of said phase by the distance calculated d (phase 160).

On the basis of the intensity revealed and initial position of theimpact, in addition to the attenuation factors of the first and secondacoustic waves (14, 15), it is finally possible to estimate the entityof damage on the pipeline 13 (phase 170).

The characteristics of the system and method for the continuousdetection of impacts on pipelines for the fluids transportation, objectof the present invention, as also the relative advantages, are evidentfrom the above description.

By contemporaneously using perceptive sensors of at least two types ofwaves, such as, for example, sensors that detect the waves propagatingalong the fluid transported and others which detect the wavespropagating along the pipeline, and by an appropriate processing of theknown data with those revealed by the sensors, it is possible tolocalize the impact even if for providing the surveys are provided atthe same side with respect to the impact point.

This system can therefore also be successfully applied for themonitoring of the coastal section of underwater pipelines or risers inproduction lines without the necessity of installing sensors at the seabottom.

Following an accurate time synchronization of the detection sensors,high precision levels are reached in measuring the time difference thatthe sensor detects the waves generated after an impact with. In thisway, an equally high precision is obtained in the localization of theimpact and all the information deriving therefrom such as intensity ofthe impact and probable effects. Finally, the distance and intensityobtained allow determining with good approximation the entity of theimpact and giving indications on the type of damage.

Analogously, the system and method for the continuous detection ofimpacts on pipelines for the fluids transportation, object of thepresent invention, can also be conveniently applied to pipelinesinstalled on land, proving to be particularly advantageous in the caseof pipelines not uniformly accessible along the whole of theirextension, for example for the installation of hydrophones. In thiscase, the use of the mixed system according to the present invention isparticularly favourable.

Finally, the system and method conceived can obviously undergo numerousmodifications and variants, all included in the invention; furthermoreall the details can be substituted by technically equivalent elements.In practice, the materials used, as also the dimensions, can varyaccording to technical requirements.

1-16. (canceled)
 17. A system for continuous detection of impacts onpipelines for fluid transportation, comprising: at least two sensorseach installed in correspondence with an end of a section subject tolength of a pipeline, wherein a first sensor of the at least two sensorsis configured to detect first acoustic waves which propagate along afirst acoustic wave transmission phase associated with the pipeline anda second sensor of the at least two sensors is configured to detectsecond acoustic waves which propagate along a second acoustic wavetransmission phase associated with the pipeline, the second acousticwaves having a different wave feature with respect to the first acousticwaves.
 18. The system for continuous detection of impact on pipelinesfor the fluids transportation fluids according to claim 17, wherein theat least two sensors are installed in correspondence with a same end ofthe section subject to detection.
 19. The system for continuousdetection of impact on pipelines for the fluids transportation accordingto claim 17, wherein the first and the second acoustic waves are diversein different propagation rates.
 20. The system for continuous detectionof impact on pipelines for the fluids transportation according to claim17, wherein the first and the second acoustic waves are diverse indifferent degrees of attenuation.
 21. The system for continuousdetection of impact on pipelines for the transportation of fluidsaccording to claim 17, wherein a first acoustic wave transmission meansis a mantle of the pipeline and a second acoustic wave transmissionmeans is a fluid inside the pipe.
 22. The system for continuousdetection of impact on pipelines for the transportation of fluidsaccording to claim 21, wherein the first sensor is a vibro-acousticsensor capable of detecting a vibratory movement which propagates alongthe mantle of the pipeline generated by an impact inside the sectionsubject to detection.
 23. The system for continuous detection of impacton pipelines for the transportation of fluids according to claim 21,wherein the second sensor is a hydrophone capable of detecting thepresence of a wave front generated by an impact inside the sectionsubject to detection.
 24. The system for continuous detection of impacton pipelines for the transportation of fluids according to claim 17,wherein the section subject to detection corresponds to a section of anunderwater pipeline.
 25. A method for continuous detection of impacts onpipelines for fluids transportation, comprising: detecting arrival offirst acoustic waves generated by an impact which has taken place in asection subject to length of a pipeline through a first sensor installedin correspondence with an end of the section subject to length;detecting arrival of second acoustic waves generated by the impact whichhas taken place in the section subject to length of the pipeline througha second sensor installed in correspondence with an end of the sectionsubject to length; determining the time difference between arrivals ofthe first and second acoustic waves; localizing the impact byidentifying its position along the pipeline on the basis of thedetermined time difference; wherein the first acoustic wave propagatesin a first acoustic wave transmission phase associated with the pipelineand the second acoustic wave propagates in a second acoustic wavetransmission phase associated with the pipeline, the second acousticwaves having different wave characteristics with respect to the firstacoustic waves.
 26. The method for continuous detection of impacts onpipelines for the fluids transportation according to claim 25, whereinthe first and second sensors are installed in correspondence with a sameend of the section subject to detection, and a localization item of theimpact calculates the distance from the first and second sensoraccording to equationd=((v ₁ *v ₂)/Δv)*Δt.
 27. The method for continuous detection of impactson pipelines for the fluids transportation according to claim 25,wherein the first and second acoustic waves differ in propagation rates.28. The method for continuous detection of impacts on pipelines for thefluids transportation according to claim 17, wherein the first andsecond acoustic waves differ in attenuation index.
 29. The method forcontinuous detection of impacts on pipelines for the fluidstransportation according to claim 17, wherein the first acoustic wavetransmission material is a mantle of the pipeline and the secondacoustic wave transmission phase is a fluid inside the pipeline.
 30. Themethod for continuous detection of impacts on pipelines for the fluidstransportation according to claim 17, further comprising: determiningthe generation instant of the first and the second acoustic wavesgenerated by the impact on the basis of the position of the impactdetermined in the localization phase, and the propagation rate of thefirst and the second acoustic waves along the pipeline.
 31. The methodfor continuous detection of impacts on pipelines for the fluidstransportation according to claim 17, further comprising: determiningdetected intensity of the first and the second acoustic waves generatedby the impact on the basis of the position of the impact determined inthe localization item and attenuation factors of the first and thesecond acoustic waves along the pipeline.
 32. The method for continuousdetection of impacts on pipelines for the fluids transportationaccording to claim 31, further comprising: estimating an entity of theimpact on the basis of the detected intensity of the first and thesecond acoustic waves, the position of the impact determined in thelocalization item and the attenuation indexes of the first and thesecond acoustic waves along the pipeline.